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Abstract
Material characterisation for finite element analysis of
rubber components
Experimental determination of the strain-energy
function of an elastomer is in general not simple, even if simplifying assumptions
are made of isotropy, incompressibility and perfect elasticity. This is
because it requires simultaneous measurement of the stresses corresponding
to imposition of two orthogonal strains which need to be varied independently
over the full range. The issue is often avoided; for example, many finite
element packages recommend using stress-strain data from uniaxial tests
to fit the constants in particular forms of strain-energy function. In consequence
the usefulness of the finite element analysis can be compromised by the
choice of an unsuitable strain-energy function. In the work presented here
an intermediate technique, based on measurement of two stresses corresponding
to a particular state of biaxial strain (shear) is used.
The technique is straightforward, although it requires
a purpose built ‘split pure-shear’ straining jig. Although, it enables a
more general form for the strain energy function to be derived, the results
support a simplifying assumption which, if made, would permit the same information
to be derived from a uniaxial test.
Strain-energy functions derived using the technique
are given for natural rubber compounds with a range of loadings of N330
black and good agreement is found with uniaxial data. The technique is also
useful for probing multiaxial relaxation and cyclic softening behaviour,
and preliminary results on these aspects are reported.
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